What is the primary feature of random sampling?

The primary feature of random sampling is that it ensures every member of the population has an equal chance of being selected. This method of sampling is crucial for reducing bias in research and ensuring that the sample is representative of the larger population. By giving each individual an equal opportunity to be chosen, random sampling helps researchers draw conclusions that are more generalizable to the entire population.

This equal likelihood of selection supports the randomness of the sample, which is fundamental to statistical validity, as it minimizes the risk that the sample may be skewed or biased in favor of certain characteristics or groups. The randomness can be achieved through various techniques, such as using random number generation or lottery methods.

In contrast, the other options reflect practices that do not align with the principles of random sampling. Selecting participants based on expertise can introduce bias by favoring knowledgeable individuals over others. Restricting selection to a specific subgroup would undermine the representative nature of the sample, and prioritizing convenience may lead to sampling bias, as it typically favors individuals who are easiest to reach rather than ensuring inclusivity from the entire population.